Materials such as plastics are commonly used for a large number of applications because of their lightness, moldability, transparency (for optical applications), workability etc. However, for many applications such as building materials (e.g. decorator panels), lightweight mirrors, windows, etc., they are relatively unsuitable because of their susceptibility to scratching and lack of resistance to chemical environmental attack. Such restrictions can be partially removed by the addition of a protective layer of glass or other suitable material on the surface or surfaces exposed to attack. Two primary difficulties exist in applying such protective layers, the first being that of achieving a sufficiently good bond between the materials, and the second being that of keeping the plastic sufficiently cool during application of the protective material to avoid deformation, melting, or surface hazing of the plastic. Furthermore, delamination (i.e. separation between the substrate layer and the protective layer) may occur upon cooling after the deposition process. The heated plastic and glass will expand during the application process, but at different rates due to different thermal coefficients of expansion. After the application process the glass and plastic will want to return to their unheated size. Again due to the different thermal coefficients of expansion, the plastic will want to contract more in size than the glass, resulting in great shearing forces. Therefore, unless the bond between the layers is sufficiently strong, delamination will occur. One means for reducing the high shear force upon contraction is to keep the plastic sufficiently cool during the application process. In this manner the plastic will experience small expansion before the deposition, resulting in small contractive forces upon cooling after the deposition.
The bond difficulty can be overcome by using graded bonding techniques such as ion beam implantation sputtering, etc. as disclosed in my Disclosure Document No. 032867, filed June 5, 1974. The overheating difficulty can be overcome by adjusting the deposition rate of a given process to the point where the energy input is below that required to raise the plastic above the deformation, melting, delamination, or surface hazing point, but for many applications the result is intolerably slow rates. The overheating difficulty can also be overcome by cooling the plastic during attachment of the glass. These two methods of dealing with the overheating problem are used if it is necessary that the protective layer be transparent and that the incoming light be unimpeded (as with non-absorbing glass) as the light passes through the structure. If, however, the application for the structure can tolerate or needs coloration as viewed from the protective layer side, or if it is to provide coloration and to control the amount of transmitted light (as in the coapplication "Light Control With Color Enhancement", Ser. No. 645,262 filed Dec. 29, 1975), the present invention allows the protective layer to be applied, if suitable application methods are used, without the need for cooling the plastic substrate and/or such that the tolerable deposition rate can be significantly increased.
With respect to a generalized deposition system, if the deposition system involves evaporation, plasma deposition or other similar methods, the source of the depositing material is either quite hot itself and/or it emits hot material. For example, evaporation uses very hot sources, which give off large quantities or radiant heat to the substrate and surrounding walls etc. and which also emit material having high thermal energy although small kinetic energy. On the other hand, systems such as cathode or radio frequency sputtering etc. have sources or emitters which can be cooled, so that the emitted material has much lower thermal energy albeit somewhat higher kinetic energy. Generally, however, in practical systems of this type difficulties in cooling the cathode (source) lead to somewhat elevated cathode temperatures of a few hundred degrees centigrade or more. More importantly, the substrates are bombarded with many energetic electrons which are extracted from the residual plasma by the potential on the substrates (or repelled by the cathode), thereby raising the substrate temperature significantly and frequently above tolerable levels. In ion plating, the substrates are bombarded with energetic ions which are used in maintaining a clean surface during deposition on the substrate.
In ion beam sputtering (IBS) (U.S. Pat. No. 3,472,751) or ion beam implantation sputtering (IBIS) (Disclosure Document No. 032867 filed June 5, 1974) the prime source of heat to the substrate is radiant heat from the ion beam target (source) since the space between the target and substrates is a good vacuum and relatively free of "residual" ions and electrons, and the emitted material has relatively low thermal energy, although relatively high kinetic energy. This kinetic energy, in practical IBS or IBIS systems, is usually not the prime factor in substrate heating. For deposition systems such as these, where the major source of heat to the substrates is infrared radiant energy from the source, the limiting factor on the deposition rate is normally the amount of heat (in the form of beam energy) brought into the target by the ion beam minus that removed by direct target cooling and/or radiation. This difference value determines the target temperature and therefore the net amount of radiated heat transferred from the target to the substrate. The object of the present invention is to permit a high rate of deposition onto the substrate without the need for cooling, while maintaining the substrate below its critical limiting temperature of deformation, melting, delamination, or surface hazing.